There are many circumstances in which it is desirable to releasably grasp the end of an elongated item so that it can be pulled along a path, such as, for example, through a length of conduit. In the electrical and telecommunication industries, for example, it is common for one or more cables or wires to be pulled through a conduit that will provide a path for the wires. These circumstances arrive particularly in the case of copper power and telecommunication wires, but they also occur with fiber optic cables, or any other type of cable or wire. The wires or cables are typically run through a path formed by a conduit that provides to the wire or cable structural protection as well as protection from environmental factors such as moisture. The conduits can include, for example, typical metal or plastic type conduits which run throughout buildings. Other examples include metal or plastic conduits that run in building foundations and underground, overhead conduits, and even various conduits found inside vehicles such as aircraft. Conduits may also run overhead through power poles or up and down the length of power poles.
Depending on the circumstances, one or even a large number of wires or cables, referred to hereinafter as “lines” maybe ultimately run through a conduit. For example, in the case of telephone lines, up to three to five hundred pairs of lines may be found resulting in one cable that is one inch in diameter. The range of conduits found in industry is quite wide, and includes, by way of example only, typical conduits from 2 inches up to 6 inches. Wires ranging for example from number 6 copper to 750 mcm copper are often found. In some cases, the copper wire will be a twisted copper wire having a relatively thin insulation surrounding the copper which itself is surrounded by ABS plastic sheathing. Aluminum wires may have a similar two layer insulation and sheathing.
Since splicing the ends of wires together can be difficult and time consuming, in telecommunications it is typically desirable to run the longest single length of line possible at a time. In many circumstances the length of line, or “run” is typically made anywhere in the range from 20 feet to 1800 feet. Also, the typical distance between junction boxes in a conduit system is 150–300 feet, so runs of at least this length are very common.
One circumstance that frequently occurs is the need to pull four electrical lines all at the same time, comprising three or four electrical lines depending on the electrical configuration, and one typically smaller ground line. These four electrical lines are often required to be pulled through a steel conduit in the form of a pipe in a building or a PVC plastic pipe underground.
In some instances when performing such a pull, the distance of the pull can become quite significant, and the force of the pull can be on the order of 500–700 pounds per line, resulting in a total pull stress of 2,000–3,000 pounds. Thus, it is desirable for a clamping system which clamps onto the end of the line being pulled to be able to accommodate the necessary force for the application.
One approach to gripping the end of a cable for a pull has been a type of clamp which uses a body that receives the end of the wire and holds it between two opposed but offset set screws. A clamp of this type is used on each wire separately where multiple wires are pulled at once. A disadvantage of this system is that the time required for insertion of the wire and proper tightening of the set screws in order to achieve satisfactory pulling can be relatively long. Moreover, if an operator does not spend sufficient time with the set screw process, or is not properly trained in setting up the system, wires may tend to slip out of the system. Moreover, some form of tightening tool such as a hex wrench is required to be present both for tightening the set screws and loosening them after the pull has been completed.
Another type of cable clamping arrangement is a basket type grip having a woven mesh that tightens around the line upon pulling force in a fashion similar to a Chinese finger puzzle. When a group of cables is to be pulled, they are typically all wrapped together and pulled by a single length of mesh. In order to provide proper gripping force, this system requires the mesh to be significantly elongated in order to have sufficient frictional force. Since the gripped length of wire typically needs to be discarded, this method can lead to a greater waste of the end of the cable than the set screw apparatus. Moreover, this system requires typically even more time and attention to attach to the end of the line or lines than the set screw device described above.
Accordingly, it would be desirable to have an apparatus and method that can conveniently and securely clamp on the end of an item to be pulled through a path such as a conduit. It would also be desirable to have such a device that can provide an adequate pulling force as needed in industry. Further, it would be desirable to have such a device that can rapidly and conveniently be used without necessarily requiring an additional tool for the attachment and release steps. Further, it would be desirable for the device to be durable and reusable.